Construction

Construction Award -- Heavy/industrial

The powerhouse and fish-passage system at Cushman Dam were completed without a single environmental incident.

Cushman Dam No. 2 North Fork powerhouse and fish passage

Location: Hoodsport, Mason County

General contractor: Harbor Pacific Contractors

Owner/developer: Tacoma Power

Primary designer: City of Tacoma

This project consisted of a new powerhouse and an innovative fish-collection and transportation system at Cushman Dam.

Harbor Pacific Contractors engineered and built the 500,000-pound concrete fish-collection structure in the dry area above the dam using a temporary frame and platform. This frame was then utilized to lower the structure into the water where it was grouted to the riverbed.

A 25-ton excavator was used, disassembled at the site and lowered down to the dam’s base for reassembly.

HPC used a negative-pressure cofferdam to contain silt from excavation and high-pH slurry from underwater concrete pours. HPC’s high-capacity pumping system pulled fresh river water into the cofferdam, preventing exfiltration. Silty and high-pH water was then pumped nearly half a mile away to a settling pond.

There was not a single environmental incident through the life of the project.